The 20th century has been a tumultuous time in psychology – a century in which the discipline struggled with basic questions about its intellectual identity, but nonetheless managed to achieve spectacular growth and maturation. It’s not surprising, then, that psychology has attracted sustained philosophical attention and stimulated rich philosophical debate. Some of this debate was aimed at understanding, and sometimes criticizing, the assumptions, concepts and explanatory strategies prevailing in the psychology of the time. But much philosophical work has also been devoted to exploring the implications of psychological findings and theories for broader philosophical questions like: Are humans really rational animals? How malleable is human nature? and Do we have any innate knowledge or innate ideas? One particularly noteworthy fact about philosophy of psychology in the 20th century is that, in the last quarter of the century, the distinction between psychology and the philosophy of psychology began to dissolve as philosophers played an increasingly active role in articulating and testing empirical theories about the mind and psychologists became increasingly interested in the philosophical underpinnings and implications of their work. Our survey is divided into five sections, each focusing on an important theme in 20th century psychology which has been the focus of philosophical attention and has benefited from philosophical scrutiny.